There is an increasing consumer demand for edible young vegetable plants, also referred to as sprouts. Sprouts may be produced by germinating seeds in either liquid medium and harvested before the cotyledons appear, as is e.g. done with alfalfa. Alternatively, seeds may be sown onto a water-soaked solid support, such as cellulose, and allowed to germinate and grow in e.g. small disposable containers until or beyond the cotyledons appear. Further growth of the plantlets may be arrested, e.g. by cooling the plantlets, usually before the plants reach a height of about 4 to 15 cm. The plantlets are then ready for consumption. Sprouts of e.g. cress, daikon (a type of radish sprout) and mustard grown this way are very popular and many other vegetables and herbs are nowadays also available in the form of sprouts. The popularity of vegetable sprouts may at least in part be explained by the notion that they are healthy. Sprouts are indeed known to be very rich in vitamins and minerals such as the vitamins C and B1, potassium, calcium, phosphorus, magnesium and iron, while at the same time they are low in calories. Daikon sprouts, i.e. sprouts of Raphanus sativa longipinatus, are particularly popular in the U.S. and in Japan were they are usually sold as young two-leafed green plants. Unfortunately, daikon sprouts do not contain anthocyanins, a compound that could further contribute to the health promoting effect of these sprouts.
Anthocyanins are present in many plants of higher order where they are responsible for the red, violet, blue or bluish black colours of flowers and fruits They are heterocyclic 2-phenyl-chromenol multiring systems (see also Formula 1) of varying hydroxylation patterns and varying absorption spectra in the visible light range. The sugar-free aglycon components of anthocyanins are referred to as anthocyanidins. They are obtained easily by hydrolysis of the glycosides contained in common fruits.
More recently, anthocyanins have drawn attention for their health promoting effects (see e.g. WO 92/03146). E.g. it is known that anthocyanins can act as scavengers for oxygen radicals such as superoxide anion radical, hydrogen peroxide, hydroxyl radical, alkoxyl radicals, peroxyl radicals, for singulett oxygen, and many other radicals. Anthocyanins have also been described as photobiological inhibitors that intervene as regulators and detoxifiers in sensitised photoreactions which take place through oxygen, thereby preventing the radical and radical chain reactions which damage cells and nucleic acids and protein molecules. Anthocyanins also protect against cell toxic and carcinogenic aldehydes such as e.g. 4-hydroxy-hexenal, 4-hydroxy-octenal, 4-hydroxy-nonenal, propanal, butanal, pentanal, hexanal, 2,4-hepta-dienal, malonic dialdehyde, and others. They even prevent the formation thereof within the framework of lipoperoxidative chain reactions. As such they may aid in the prevention of cancer or may delay the effects of ageing. Furthermore, they detoxify the acetaldehyde resulting from ethanol decomposition and the formaldehyde resulting from methanol decomposition.
Some species of Raphanus do produce anthocyanins, as is most notable from the red colour on the outside of the radish varieties as usually sold in Europe and the U.S. However, no Raphanus sprouts are available that contain appreciable levels of anthocyanins. Thus, it is an object of the present invention to provide for Raphanus plants containing increased levels of anthocyanins, in particular, it is an object of the present invention to provide for Raphanus plants, the sprouts of which contain increased levels of anthocyanins. Advantages of the anthocyanin containing sprouts of the invention over other consumable anthocyanin sources, such as e.g. fruits like blueberry or grapes, include (1) the much shorter cultivation time; (2) the relatively high concentration of anthocyanins in the sprouts allowing to consume only small amounts of the sprouts to meet a certain anthocyanin intake; and (3) the great variety a dishes and recipes in which the sprouts may be applied.